FIELD OF THE INVENTION
The invention relates to a chain conveyor for a sheet-processing printing machine having conveyor chains bearing gripper systems for transporting sheets, the chains being revolvable, during operation, along closed chain tracks having at least substantially circular segment-like chain track sections, and a guide rail device for guiding the conveyor chains; the invention also relates to a printing machine equipped with the chain conveyor.
A chain conveyor of the type mentioned in the introduction hereto has become known, for example, from the published German Patent Document DE 39 39 250 C1. A proposed invention therein, wherein the direction of curvature of a chain track remains constant between transfer points on deflection guides, is based upon a solution to the problem that the conveyor chains change from making contact with an outer guide rail to making contact with an inner guide rail or the reverse, respectively, with the production of a great amount of noise, if changes of direction are provided in the chain track. In this regard, a change of direction is obviously understood to mean that the chain track passes through a turning point. However, a further extremely critical region of a chain track is located so that it follows an at least substantially circular segment-like chain track section within which the gripper systems borne by the conveyor chains are subject to relatively high centrifugal forces at the high processing speeds which are common these days in powerful printing machines. These centrifugal forces may result in the gripper bars, which bear the grippers of the gripper systems, being bent radially outwardly relative to the circular segment-like chain track section, the gripper bars then swinging back in the opposite direction when the chain links bearing the gripper systems leave the circular segment-like chain track section and enter a chain track section having a smaller curvature than that of the circular segment-like chain track section, or having a substantially rectilinear course. Consequently, an inner guide rail that follows the circular segment-like chain track section is subject to severe impact impulses from those sections of the conveyor chain which are connected to the gripper systems. Not only does this lead to the production of a great amount of noise, but it also has a considerable wearing effect that causes damage initially to that point on the inner guide rail which is exposed to the impact impulses and, subsequently, also in less highly stressed sections of the guide rails and finally also to the conveyor chains.
Sudden dissipation of the aforementioned centrifugal forces is admittedly already countered by configuring the chain track so that, adjacent to a circular segment-like chain track section, a chain track section is provided having a course initially formed with a greater radius of curvature than that of the circular segment-like chain track section, so that a stepwise reduction in the centrifugal force results.
For the case wherein the circular segment-like chain track section is implemented by a sprocket around which a conveyor chain is wrapped, in order to achieve the aforementioned stepwise reduction in centrifugal force, in the outlet region of the circular segment-like chain track section, the conveyor chain is guided both by the sprocket and by a guide track that is arranged directly alongside the latter and is formed on an inner guide rail, the guide track, as viewed in the direction in which the sprocket revolves, initially running within the root circle of the sprocket and then gradually lifting the chain out of the sprocket. However, during the action wherein the chain is lifted out of the sprocket, the chain rollers of the roller chains which are commonly used in chain conveyors of the foregoing general type are firmly held in the tooth gaps formed in the sprocket while they slide over the guide track effecting the lift-out action. This also leads to wear of guide rails and chain rollers, however.